You can use either the Delegated Administrator Console or Utility:
Delegated Administrator Console
In the Delegated Administrator Console, use the Create New User wizard. (Click New in the User List page for the organization where the user is to reside.) For more information, see the Delegated Administrator Console online help.
Delegated Administrator Utility
Use the commadmin utility user create command. For example, to add user jdoe in the sesta.com domain:
commadmin user create -D calmaster -F John -n sesta.com -k hosted -l jdoe -w calmasterpassword -W jdoepassword -L Doe -S cal -B red.sesta.com -E email@example.com
For details on all the available options for the commadmin utility, refer to the Sun Java System Communications Services 6 2005Q4 Delegated Administrator Guide